Photos freezes when I try to delete some pics

Please read the following user tip and restate your question/problem in detail: Writing an Effective Apple Support Communities Question - Apple Community  

As a test launch Photos with the Option key held down and create a new, test library.  Import some photos and test to see if the same problem persists. Does it? (This tells us if the problem is limited to your current library or is more wide spread)

Next log into another user account, Set up users, guests, and groups on Mac,  and see if the problem persists (this tells us if the problem is limited to your user account or is system wide).

Boot into Safe Mode (How to use safe mode on your Mac - Apple Support) by booting with the Shift key held down and check there to see if the problem persists.  Reboot normally and test again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing. 

Since you can use Photos OK in the other user account there's something in your account that's may be the culprit. Download and run Etrecheck. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Add Text button to include the report in your reply. How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report

IMPORTANT:

Before running Etrecheck assign Full Disk Access to Etrecheck in the app's Privacy preference pane so that it can get additional information from the Console and log files for the report:

ALSO IMPORTANT:

Then we can examine the report and see if we can determine the root of the problem.

There's nothing in the report that's suspicious. Do you the iCloud Library enabled? If not double click on your problem library with the Option + Command keys held down to repair the library if possible.

Photo stream seems to be causing this kind of problems in Photos 5 on macOS 10.15.

Several users have reported, that they had problems deleting photos, as long as they have been using my Photo Stream.

My Photo Stream is no longer suitable to transfer photos from iPhones and iPads, because it has never been updated to support videos or Live Photos. Users with a new AppleID cannot even enable it at all.

Do you have a backup copy of the library made just prior to your updating to 10.15.4? If so restore it and try opening with Photos.